Development of an Original Multi-Physics Model for Predicting the Degradation of Photovoltaic Module Performance Under Nigerian Tropical Climate Conditions

Photovoltaic module degradation under tropical climate conditions involves coupled thermo-mechanical stress, photochemical degradation, humidity ingress, and soiling processes that interact in ways inadequately captured by existing empirical lifetime models calibrated for temperate European or North American climates. Accurate prediction of Nigerian tropical climate degradation rates is essential for solar project financial modeling and for informing warranty standards in the Nigerian renewable energy market. This research develops an original multi-physics computational model for photovoltaic module degradation under Nigerian tropical climate conditions, integrating electrothermal, hygromechanical, photodegradation, and soiling physics modules in a unified simulation framework. Thermal stress finite element simulations using measured Nigerian tropical temperature cycling profiles as boundary conditions are coupled to moisture diffusion models parameterized from measured water vapor transmission rates for Nigerian market encapsulant materials. Ultraviolet-induced EVA encapsulant yellowing is modeled using a modified Arrhenius photodegradation kinetics scheme recalibrated against accelerated weathering test data conducted on modules from six manufacturers deployed in Nigerian installations. An original degradation superposition theorem is derived and proved mathematically, demonstrating that under specific conditions the multi-physics degradation modes are linearly superposable, significantly simplifying computation. The model is validated against a seven-year outdoor performance dataset from 24 modules at monitoring stations in Lagos, Abuja, and Kano. Predicted annual degradation rates of 0.82 to 1.24 percent per year are within measurement uncertainty of observed rates. Design guidelines for enhanced module durability in Nigerian tropical climates are derived. Keywords: photovoltaic degradation, tropical climate, multi-physics model, module lifetime, Nigeria